1. Field of the Invention
The present invention relates to polymeric products and, more particularly, relates to polymeric products which electrodeposit on the cathode.
2. Brief Description of the Prior Art
Electrodeposition of aqueous organic coatings has risen to industrial prominence in recent years. The process has many advantages, including uniformity and completeness of coating, even on intricate shapes. Virtually any electroconductive substrates may be coated, although the process has been primarily employed to prime or one-coat ferrous metal substrates.
Particular interest has recently arisen in electrodepositable coatings which deposit on the cathode. Cathodically deposited coatings appear to have better corrosion resistance than anodically deposited coatings. In addition, during anionic electrodeposition, oxygen and metal ions are evolved at the anode which may discolor the depositing coating. At the cathode, however, only hydrogen is evolved which has no detrimental effect on the depositing coating.
For electrodeposition on the cathode, most coating systems are based on polymers containing cationic salt groups. One particularly interesting class of polymer are those containing quaternary ammonium salt groups derived from reacting polyepoxides, such as a polyglycidyl ether of a polyphenol with tertiary amine salts. An example of these types of resins is disclosed in U.S. Pat. No. 3,839,252 to Bosso and Wismer. These resins, for the most part, are prepared with mono-tertiary amine salts and diepoxides and have the charge groups located in the terminal portions of the polymer molecule. Although these particular polymers are eminently suited for use in cationic electrodeposition, currently being employed commercially in many industrial electrodeposition coating applications, they are limited in the charge content attainable. Higher molecular weight species also have higher equivalent weights and this limits the dispersibility of the polymer.
The present invention can be looked upon as an improvement on the resins disclosed in U.S. Pat. No. 3,839,252. In the present invention, the resins are internally ionized with the charge groups being positioned along the polymer chain not only in terminal positions but also in the middle portions of the polymer chain. Thus, high molecular weight products with relatively low equivalent weights can be prepared. The products of the invention are very dispersible, making them particularly attractive candidates for electrodeposition.